Per the table below from the LoRaWAN Regional specification, the first LinkADRReq command performs the following function: The ChnlCntl value of 7 disables all 125kHZ channels and then applies ChnlMsk of 0100 which enables the first 500 kHz channel: 64 (0000 0001)

For the second LinkAdrReq, the ChnlCntl equals “0” meaning it applies to channels 0-15 with the first 8 being enabled.
To further illustrate: To enable the entire bank of 16 channels the first ChannelMask would be 0300 - 0000 0011) - So, the full command would look like - LinkADRReq ChnMsk 0300 ChnlCntl=7, LinkADRReq ChnMsk=FFFF ChnlCntl=0
In addition, the Data Rate, Tx Power, and NbTrans values from the last LinkAdrReq (second in this case) command are what is enabled by the device